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question regarding DC link inductors for ZVS circuit

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Ash Small

Sun Aug 19 2012, 09:33AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

You seem to have grey with a yellow top which is something else entirely.

These are definitaly green with yellow top, it also shows up as green on my (Compaq) screen.

Thanks for the input again Steve, they had yellow/grey and green/blue at the hamfest, I wish I'd known.

Micrometals has the T106-40 cores listed,Al 80.1. (40=green/yellow). Apparently it's the cheapest material they supply.

Material characteristics for -40 is here;

Unfortunately I don't know what properties to look for in an ideal DC link inductor. (Hence the purpose of this thread........)

m4ge123

Sun Aug 19 2012, 10:14AM

Registered Member #4118 Joined: Mon Oct 03 2011, 04:50PM
Location: MD
Posts: 140

As you can tell from the graphs, #40 is very similar to #26 and #52 (yellow/white and green/blue respectively). It should work fine.

Ash Small

Sun Aug 19 2012, 11:13AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Well, thanks to everyone who has contributed to this thread. I now know that the cores I have should work ok.

But, for the benefit of others in the future, what general properties are we looking for, and what factors should we consider when buying cores for this task?

I know most will work to some extent, but some get hot (wasting power), etc.

So many problems associated with this circuit have been attributed to people choosing the wrong core.

What are the ideal qualities that we should be looking for? (these cores cost next to nothing, blown mosfets,etc. cost consderably more, not to mention the frustration incurred when this circuit fails to work as expected.)

I'm trying to approach this scientifically, using a bit of maths, rather than just 'suck it and see'.

Steve Conner

Sun Aug 19 2012, 02:50PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

The qualities you should be looking for are yellow/whiteness or green-blueness.

These materials are designed for DC filter inductors in switch mode power supplies.

Ferrite E-cores are also acceptable if you use an air gap.

Ash Small

Wed Aug 22 2012, 08:44AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Steve Conner wrote ...

The qualities you should be looking for are yellow/whiteness or green-blueness.

These materials are designed for DC filter inductors in switch mode power supplies.

Ferrite E-cores are also acceptable if you use an air gap.

I found this on Uzzor's site:

"Powdered iron cores are generally color coded, and most often with two different colors. Ferrites on the other hand tend to be a single color, or unpainted. "

It looks like, as a general rule, torroidal cores which are two colours are better suited to this application than single colour cores.

GeordieBoy

Tue Aug 28 2012, 11:06AM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Micrometals Type-40 is a Hydrogen reduced iron-powder much like the yellow/white (Type-26) and green/blue (Type-52) cores Steve Conner suggested.

Any of these material grades should work fine for your DC link choke up to 500kHz or so. Since your cores are small but you have more than one core available, you can always stack cores side-by-side and wind around the stack to get the combination of inductance and resilience to DC saturation that you require.

-Richie,

Daedronus

Tue Aug 28 2012, 12:31PM

Registered Member #2329 Joined: Tue Sept 01 2009, 08:25AM
Location:
Posts: 370

A question that hunted me for some time regarding DC filter inductors...
Do you need to use litz wire with proper diameter for the sink depth at the ripple frequency? Or a single big fat wire is Ok considering the majority of the carried current is DC?

GeordieBoy

Tue Aug 28 2012, 02:46PM

Registered Member #1232 Joined: Wed Jan 16 2008, 10:53PM
Location: Doon tha Toon!
Posts: 881

Or a single big fat wire is Ok considering the majority of the carried current is DC?

I think you've answered your own question

Whether you really need to use Litz depends on what the ripple current is. The purpose of a choke is to allow the passage of considerable DC current whilst limiting AC ripple, so in general the DC current will be large and the AC current will be comparatively small. This makes the larger copper fill of a solid conductor more efficient than the individually insulated bundles of Litz with the same overall OD. It's also cheaper.

Iron-powder cores tend to be quite lossy for rapid large flux excursions, so I'd go as far as to say that you would want solid copper for iron-powder chokes that normally run in continuous-current mode with quite a small percentage of actual ripple current. If the ripple current got bigger you'ld likely notice the core overheating before skin losses in the copper.

If the desired ripple current is actually a large percentage of the DC current, (like when running a SMPS choke in discontinuous current mode,) a gapped ferrite core will be less lossy than iron-powder, and Litz wire may then be more efficient for carrying the combined AC+DC current.

In a recent active PFC front-end I designed I used "ripple-steering" where one winding on the PFC boost choke was done with single core copper wire to carry the line-frequency current, and the other ripple-steering winding was made with Litz wire to support the modest AC ripple current in this design.

You use the cheapest cores and winding regimes you can get away with for the job!

-Richie,

Patrick

Tue Aug 28 2012, 07:49PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

those mains freq toroidal transformers are nice, id hate to see them trashed for a simple device. youd be wiser (in my opinnion) to save them for one of your other greater projects. 30 volts at 3 amps could be used for many other apps that youd rather not series a bunch of batteries for.

Ash Small

Tue Aug 28 2012, 08:22PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

GeordieBoy wrote ...

Micrometals Type-40 is a Hydrogen reduced iron-powder much like the yellow/white (Type-26) and green/blue (Type-52) cores

Thanks for the input Richie.

A few webites, such as this one:

say the following, or similar:

"Iron powder core, MnZn NiZn core, Toroidal core, Ferrite core, Metal core, Ferrite magnet core, ceramic ferrite magnet,Iron powder,Iron Powder Core -40 Green/Yellow,Magnet"

I assume that by mixing MnZn and NiZn in the correct ratio, you get a core with similar properties to the iron powder core you mention.

as mine came from a stall at a hamfest I've no idea what make they are, just that they are type 40.

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